1. Field of the Invention
The present invention relates to communication cables. More particularly, the present invention relates to a fiber optic cable, suitable for connection to a moving object used in deep-sea exploration.
2. Description of the Related Art
A remotely operated underwater vehicle (ROV) is known in the prior art. An ROV is typically operated by a person aboard a ship or submarine, and is tethered to the ship or submarine by at least a power cable and a communication cable. The power cable supplies power for ROV motors, lights, cameras, manipulation arms, etc. The communication cable carries control signals to the ROV for maneuvering the ROV, and information signals from the ROV to the operator, such as video signals, sound signals, temperature readings, equipment diagnostic signals, etc.
An ROV can be used to investigate and retrieve samples of undersea plant and animal life, and to explore and retrieve wreckage at the bottom of the sea. An ROV is also useful to inspect and repair undersea pipelines, cables, structures of an oil rig or dock, a hull of a seagoing ship or submarine, etc.
The undersea environment of an ROV is harsh, with the presence of salt water, water current forces, temperature extremes, rapid temperature fluctuations, extreme pressure, and the physical encountering of foreign objects. Therefore, there exists a need for a communication cable which is particularly immune to the undersea environment and which can perform well as the ROV undertakes its various undersea tasks.
Fiber optic cables are excellent communication cables. Fiber optic cables are capable of high-speed data communication over an extended bandwidth with very low attenuation over long cable distances. Various fiber optic cable designs are known.
For example, U.S. Pat. No. 5,627,932 of the present assignee illustrates a reduced diameter indoor fiber optic cable. As illustrated in FIGS. 1-2, the first prior art cable 10 includes a single optical fiber 11, containing a core and a cladding layer surrounding the core, with one or more polymer coatings applied over the cladding, such that the optical fiber 11 assumes a diameter of 250 um. The optical fiber 11 is surrounded and bonded to a coating or tight buffer layer 12, wherein the outer diameter of the tight buffer layer 12 is 500 um. A layer of loose tensile strength members 13 surround the tight buffer layer 12. Finally, an outer jacket 14 surrounds the strength members 13 and has an outer diameter of not greater than 1500 um. The tight buffer layer 12 and the outer jacket 14 are formed of polyvinyl chloride (PVC).
U.S. Pat. No. 5,627,932 also illustrates a reduced diameter indoor fiber optic cable having two optical fibers. As illustrated in FIGS. 3-4, the second prior art cable 20 includes two optical fibers 21, each containing a core and a cladding layer surrounding the core, with one or more polymer coatings applied over the cladding, such that the optical fiber 21 assumes a diameter of 250 um. The optical fibers 21 are each surrounded and bonded to a coating or tight buffer layer 22, wherein the outer diameter of the tight buffer layer 22 is 500 um. A layer of loose tensile strength members 23 surround the two tight buffer layers 22. Finally, an outer jacket 24 surrounds the strength members 23 and has an outer diameter of not greater than 2000 um. The tight buffer layers 22 and the outer jacket 24 are formed of PVC.
CommScope, Inc., the assignee of the present invention, presently markets a fiber optic cable similar to the one illustrated in FIGS. 1-2, known as a riser simplex cable. FIGS. 5 and 6 illustrate the riser simplex cable 30. The optical fiber 31 contains a core and a cladding layer surrounding the core, with one or more polymer coatings applied over the cladding, such that the optical fiber assumes a diameter of 250 um. The optical fiber 31 is surrounded and bonded to a coating or tight buffer layer 32, wherein the outer diameter of the tight buffer layer 32 is 900 um (instead of 500 um, as discussed above). A layer of loose tensile strength members, in the form of aramid yarn 33, surround the tight buffer layer 32. Finally, an outer jacket 34 surrounds the aramid yarn 33 and has an outer diameter of not greater than 2900 um. The outer jacket 34 and tight buffer layer 32 may be formed of PVC or low smoke zero halogen compounds (LSZH).
The cables described above in conjunction with FIGS. 1-6 are well suited for indoor use, but are not suitable for undersea use. Several years ago, CommScope, the assignee of the present invention, marketed an undersea cable 60 similar to the one illustrated in FIGS. 3-4, which was modified for undersea use. FIGS. 7 and 8 illustrate the undersea cable 60, which includes two optical fibers 61, each containing a core 62 and a cladding layer 63 surrounding the core 62, with one or more polymer coatings 64 applied over the cladding layer 64, such that the optical fiber 61 assumes a diameter of 250 um. The optical fibers 61 are not surrounded by a coating or tight buffer layer (like buffer layer 22 in FIGS. 3 and 4). Rather, the optical fibers 61 are directly surrounded by loose tensile strength members 65 and a Carnation light mineral oil 66. Finally, an outer jacket 67 surrounds the strength members 65 and Carnation light mineral oil 66.
Applicants appreciated drawbacks in the undersea cable 60 of FIGS. 7-8. For example, the undersea cable 60 was susceptible to signal attenuation, because two optical fibers 61 are suspended alongside each other and strength members 65, which can lead to a micro-bend situation. A micro-bend occurs when an optical fiber incurs a sharp deformation when pressed against an adjacent solid or semi-solid object (e.g., the adjacent optical fiber 61 or one or more strength members 65). The deformation can result in significant signal loss, e.g. light escapes through the cladding layer 63 at the point of the deformation, which leads to an overall signal attenuation.
Also, Applicants appreciated a need in the art for a new design of undersea cable with an improved hockling resistance and tensile strength and better protection for the optical fiber, as compared to the undersea cable 60. Hockling is the formation of spiral loops in the cable when lengthwise tension is relaxed.